Craig Sawyers

I've been peering at the photos of the original T2, and the only difference I can find after a couple of hours is that pin 9 (the shield between the two halves of the triode) is connected to ground in the original, but not in the clone. Also Stax use a grounded shield tube around each 6DJ8. I've also been searching the web for the significance of connecting pin 9 to ground, or not. Most audio applications ground it, but it is uncertain whether this has a grounding in theory or not. The changes in interelectrode capacitance seem trivial from the datasheet. But I also read that the 6DJ8 was originally introduced as a TV RF stage, and that with its high mu if it can burst into self oscillation it will. Most folks seem to add a 1k grid stopper to quite the things down. So maybe pin 9 to ground and a shield are important in taming the 6DJ8, particularly in an ultrahigh bandwidth cascode/constant current arrangement. Plus perhaps a grid stopper tight up to the pin, although that would need a track cut, and wasn't necessary in the orignal.

Inu, what adjustment protocol did you use? ie where to preset RV1 and RV2, and which order in which to adjust, whether they need to be adjusted simultaneously or not, etc. And how many meters, and connected where? Apart from KG, I seem to be number 2 to get to this stage (you were first), and we need to work out a foolproof method of setting this beast up to prevent auto-destruct setting of the battery pots, or there will be a further 17 learning curves down the line, and buckets of dead silicon.

That is very useful information Inu. I am using old stock Mullard ECC88/6DJ8, probably 1960's vintage. They measure fine on a tube tester, but maybe the T2 is sensitive regarding input tubes. As Kevin mentioned before, adjust Active Battery is tricky. While adjusting the active batteries, you will better to monitoring voltage between +/-Out to GND or +Out / -Out at same time. Not necessary to adjust it to exact 740V. My unit is balanced at 749 – 750V. If adjusted point of the RV1(2K) is out of the safe area, loud buzzing noise comes from the ear speakers. It sounds like oscillating and very loud. Turn both RV1 quickly to find the point that stop the loud noise.

Wierd is right. The channel that is nominally working still has a pair of dead LED's in one of the current triples. The more I think about it, it just has to be a tube issue. Everything that died on the deceased channel was associated with one of the EL34's. I'll do some more serious checks on those tubes and see if I can find out if that is the problem, although I can only get to 400V anode-cathode voltage on my tester (AVO CT160). JFET's are GR Idss band, which is what was called for. But even if the Idss band was an issue, it wouldn't explain mass silicon suicide. Anyway, I've just ordered a bucket full of spare semiconductors. Enough to fix the sucker, and plenty left over (which of course I'll now never need). After all, what is another hundred quid on this beast?

I'd like to think so. But I don't think that is the case - the only dead LED's that I have found are the ones in the current triples. I'm wondering whether it is something to do with the EL34's I'm using. Not minded to put in new tubes for the first run, I used a serviceable old pair - just running one channel at a time. Now those tubes measure pretty much OK - but they could be just off enough, or have some odd electrode short that doesn't show up on test, to trigger a problem. I'll fix the unit up, replacing the LED's as a matter of policy, and use new EL34's. It'll be a few days since I don't have spares for the FETs. Not the best of days....

Well this is interesting. The channel that self oscillated itself to death has for certain dead: Two dead 2SK216 (the ones in the cathode circuit) One 2SJ19 Two 100V zeners One 2SC3675 - the one in one of the 740V batteries Several dead LED's associated with the current sources. The last is interesting, because in one case only *one* of two series connected diodes is dead. This was established by using a 9V battery and 5.6k series resistor. In the channel with stuck battery voltage there is also at least a pair of dead LED's in one of the anode current sources (the pair associated with the current triple). Which would explain completely why I could not adjust the battery voltages. There are no other dead semiconductors in that channel (at least that I have thus found). All the power supply voltages are correct.

You know - that just happened to me. Uncertain what caused it in my case, but was merrily adjusting the active battery, both test points at very close to 740V, then a sound of oscillation (whistling noise). Never a good sign - then crack - certainly 2SK216 are fried. The other channel refused to adjust. Stuck at about 560V no matter what I do (-540, +20 WRT 0V).

That Al does sound really awful. But Doug's comment for some reason made me think of Dr Stragelove....

Well, I tried and failed to get the beast finished before wife and daughter got back from Rhodes. What I do have now is all four Amphenols pigtailed and installed in the now completed chassis. With that in mind, you have to leave the Amphenol fixing screws loose, plug in the umbilical to centre the chassis connector in the hole and then fully tighten the nuts. So only the internal wiring to complete now.

Ah - you spotted that lurking in the background

Just the Amphenols to wire up now http://www.tech-enterprise.com/tekstuff/P9070512.JPG http://www.tech-enterprise.com/tekstuff/P9070513.JPG

Over the years so many useful devices have just vanished. Dangerously unprotected MOSFETs from Siliconix that were essential in certain CCD designs - long dead (came with a wire clip shorting the leads together. Solder in and then remove clip). Sensible dual FET's like the 2SK389/2SL109 - dead. Now pretty much the only 900V PNP - dead. Next on the death list will be components with leads, with surface mount being the only game in town. Lead free solder? A complete sham, which subject I can wax lyrical on at length. One audio manufacturer I know has a reel of lead free solder on the bench for audit purposes, and then uses Wonder Solder or some such leaded solder in building the gear. Don't even get me started on the name change game - Hitachi to Renesas, Motorola to ONsemi, HP to Agilent to Avago. Without even considering the number of useful products that have gone the way of dust as a result of Vishay's quest to own every brand going - then doing "product rationalisation". <soap box mode> = "off"

OMG - I've just been trawling Sanyo's various sites, and eventually found the discontinuation notice Discontinued products property Dead for good at end December 2010, with final order submissions by end September. Good job I had enough stock for the BH; and thirty odd lurking in a bag recovered from an aborted project (don't ask).

Goddit!

?? On other topics, I was merrily torquing down the devices on the amp board, with the torque screwdriver set to the correct value of 1.1Nm for TO220 packages. I then moved on to the 2SA1486's - and promptly split the first one in two. Then I checked - the maximum torque for a TO126 package is 0.4Nm, and use of a washer under the screw head is recommended to further spread the load. Taking those remedial actions all is OK. By the way, I have gone back to using steel screws, but with the Aavid 7721-3PPSG bushes. These have a 3.18mm (1/8") shaft, which goes pretty much all the way through the 4171G ceramic insulators. The steel screws mean that you can get the torque set for maximum heat transfer (with heatsink grease too of course). The 7721-3PPSG is a slip-fit in some device holes and a tight interference fit in others - tolerance stack up I guess. Also, they cannot be used for metric screws because the hole is not quite big enough - so for that insulating bush those of us in metric countries need to get hold of the imperial 4/40 screws and nuts specified in the BOM. What I am doing with the 2SA1468's is to put a 4.7mm length of heatshrink over the threads of the 4/40 screws. This makes a nice fit in the device hole. 4.7mm goes most of the way through the ceramic insulator.

I got mine from Future Electronics.

Geez - I've just spent five hours (a) fitting the DACT and ( fitting half the transistors to the heatsinks (just the 20-off c3675's). Gotta get it more or less finished tomorrow - wife and daughter have gone to Rhodes (I hate hot holidays; I'm a cool climate guy) so I've been using the week as play time. They come back Wednesday, and will expect to find the house not looking like an electronics production shop floor.

Geez - no wonder I couldn't find it! The really stoopid , shot in the foot thing is that quadsunlimited was credited a few posts down. In fact the whole discussion was very pro the work he'd done in stacking. Feels kind of different now, doesn't it?

Apart from the fact I cannot find the mail from John Buchanan to which you are objecting, what precisely is your point? Whichever way you look at it you just got free advertising. And just to be perfectly clear, did you join this forum to make just that one post?

Whohoa! Power supply lives. Just went for broke, screwed the whole shebang into the casework, wired it up and turned it on. Unloaded volts are just about bang on. Haven't checked for ripple yet Now the question is - do I dummy load it, or just go for broke and build the amp up?

Rigoletto. Series of live performances from the locations that Verdi set the opera in, in Padua. Placido Domingo as Rigoletto, with remote orchestra conducted by Zubin Mehta. First act was last night, second was midday today, and final act tonight at 10:30. Amazing. I watched a similar exercise around 20 years ago of Tosca, again with Domingo, set in the correct settings around Rome. Final act was 4am - that one needed some stamina to watch.

There are some versions of the BOM lurking earlier in the thread. But I'm a relative newcomer to this electrocution-grade amp thread - I've been concentrating on KG's ultimate madness - the T2. Just got the power supply board and three transformers mounted in the power supply chassis. Without the front and top it is nearly a hernia lift - it is Krell-like mass, must be 30lbs+. And then there is the amp.... That animal operates from +500 to -560V rails, plus others at 250V, -260V, +/-12V. I'm really taking my time and doing the build with real electrical best practice - there is just no room for error, or getting a finger in the wrong place. But somewhere not too distant down the line, I'd like to have the option of building the KGSSHV - hence the request for a board set. I has just got to be cheaper and easier than the T2, which runs to several thousand of whatever currency takes your fancy, and more construction hours than a sane man can safely contemplate.

Massively off-topic, but..... A branch of my family did just that, in 1921. Looking forward to a life in the coal mines of North East England, Adam McKinght uprooted his family (wife and two children) and off they went to Vancouver. And there that branch of the family live to this day. Actually 80 years previously to that, his grandparents escaped from Ireland just at the start of the potato famine in the 1840's, and found their way to the NE to become coal miners. Given these traumatic events, I'm sure they ended up with a much better life (Adam McKnight opened a general store in Nanaimo; better for sure than hewing coal). And yes - I got heavily into family history a few years ago.

Nah - I couldn't cope with imperial measurements on a day to day basis

Yes - because the part is made in the US, then has to travel several thousand miles to get to Farnell. So I can either buy at half the price from Digikey, then pay shipping to the UK plus tax, then wait a week for them to arrive, and then drive 40 miles round trip to collect from Parcel Force to pay the tax. Alternatively I can get them the next day from Farnell, cheaper in overall terms (no 40 mile round trip etc etc). The only place that really has international trade sorted out is Mouser. They have arranged with UK customs to charge tax in advance, then offer free shipping for orders over $100. On a big project, peppered with Dale resistors and other fancy stuff, I can order on line and the damned stuff arrives from the US through my mail box two days later. Digikey has something to learn.